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    <script>
        //     1、求1 + 2！ + 3！ + 4！....+20!的值
        // 2！ = 2 * 1
        // 3！ = 3 * 2 * 1
        var n = 1
        for (i = 1; i <= 20; i++) {
            n = n * i


        }
        console.log(n)
    </script>
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